In recent years, inkjet recording devices, which are inkjet type image recording devices, have come to be used more than gravure printing type or flexo printing type devices, which require prepress process, because inkjet type image recording devices allows easy and inexpensive image forming.
In the field of image recording on commodities or packing materials for commodities by the use of such an inkjet recording device, materials such as resins or metals without ink absorbance are often used for commodities or packing of commodities. As inkjet recording devices that fix ink to a recording medium of such a material having no ink absorbance, inkjet recording devices of UV-curing type which uses UV-curable ink are known.
In general, in an inkjet recording device of UV-curable type, UV light is projected to UV-curable ink having landed on a recording medium so that the UV-curable ink is cured and fixed to the recoding medium. Herein, when the amount of UV light projection to a printing part is small, ink deposited on the recording medium somewhat spreads, resulting in creation of gloss. Conversely, when the amount of UV light projection is large, ink deposited on the recording medium spreads little, resulting in creation of a mat tone.
There is known an inkjet recording device that controls the amount of UV light projected onto a printing part to control the dot tone after printing so that a printing result is obtained in which gloss or mat tone is adjusted (Patent Document 1). A shutter is arranged at an opening, on the recording medium side, of a UV light emitting device in this recording device, wherein the opening degree is arbitrarily set to enable control of the amount of UV light projection onto a recording medium.
[Patent Document 1] TOKKAI No. 2004-1327
However, in an inkjet recording device that uses UV-curable ink, it is possible that UV-light for curing ink randomly reflects to parts other than a printing surface, for example, onto the-nozzle surface of a recording head, resulting in curing ink deposited on the nozzle surface to cause a jetting failure or the like. On the other hand, it is necessary to arrange a UV light emitter near recording heads so as to obtain a high image quality by curing ink immediately after printing. A carriage may be provided with a mechanism such as a light trap for absorbing or attenuating reflected light. However, it is impossible to absorb or attenuate all of reflected lights, and tiny reflected lights reach the nozzle surface of a recording head due to diffused reflection or the like.
Therefore, as is known, recording heads are maintained in order to remove ink deposited on the nozzle surfaces. Herein, UV-curable ink is applicable to any type of recording medium, allowing it to perform printing on any recording medium. However, the surface roughness and reflection rate are different depending on the recording medium. Therefore, the amount of light energy of reflected UV light reaching the nozzle surface of a recording head may be greater depending on the type of a recording medium even if the UV light projection time is the same. Therefore, if the maintenance interval is set to be the same all the time, there is a problem that the maintenance interval is too long for a recording medium which causes a large amount of light energy of reflected light.
Particularly, cation-curable ink has a characteristic of accumulating light energy, and accordingly even in the case of light energy in a tiny amount, light energy is accumulated as time elapses to finally cure the cation-curable ink. Further, ink having been cured once cannot be removed by maintenance. Therefore, it is necessary to perform maintenance before UV light projection time exceeds a certain time period.
However, on the other hand, if maintenance interval is shortened for any recording medium, maintenance is performed frequently to consume a lot of time for maintenance, resulting in drop in printing rate on a recording medium by the inkjet recording device. Further, as maintenance consumes ink, too frequent maintenance causes a problem of wasting ink a lot.